This invention relates to a locking device in a gas spring of the type comprising a cylinder, a free piston dividing the interior of the cylinder into a gas chamber and an oil chamber, and a piston having a piston rod and slidably disposed in the oil chamber.
When a gas spring of this type is equipped in a chair or the like it is required to adjust the overall length of the gas spring and to lock it at the adjusted position. For this end, it is usual to incorporate a valve in the piston for controlling oil flow across the piston. The valve is operated from the outside of the cylinder and, when the valve is closed, oil flow across the piston is prevented and the movement of the piston rod relative to the cylinder is prevented. But such prior art gas spring has shortcomings such that it is very difficult to prevent oil leakage across the valve and a piston seal and that the construction of a valve operating mechanism is complicated and expensive.